This invention relates to newly identified polynucleotides, polypeptides encoded by such polynucleotides, the use of such polynucleotides and polypeptides, as well as the production of such polynucleotides and polypeptides. More particularly, the polypeptide of the present invention is human Inositol Monophosphatase H1, sometimes hereinafter referred to as xe2x80x9chIMP-H1xe2x80x9d. The invention also relates to inhibiting the action of such polypeptides.
Cells respond to extracellular stimuli through complicated networks of responses. Inositol lipid metabolism plays a key role in intracellular signalling. Agonist-induced stimulation of cells releases the signalling molecules diacylglycerol and inositol polyphosphates via phospholipase C hydrolysis of phosphoinositides. Diacylglycerol functions to stimulate protein kinase C (Nishizuka, Y., Science, 233:305-312 (1986), and several inositol polyphosphates, most notably inositol 1, 4, 5-triphosphate evoke the release of intracellular and intercellular calcium (Berridge, M. J. and Irvine, R. F., Nature, (London), 312, 315-321 (1984). Action of inositol phosphatases and kinases gives rise to a plethora of inositol phosphates (Majerus, P. W. et al., J. Biol. Chem., 263:3051-3054 (1988) in the cytosol that may also serve as signalling or regulatory molecules.
Inositol monophosphatase (IMP) plays an important role in the phosphatidylinositol signalling pathway by catalyzing the hydrolysis of inositol monophosphates. IMP""s are believed to be the molecular site of action for lithium therapy for manic-depressive illness. Lithium inhibits inositol monophosphatase and prevents the accumulation of free inositol from inositol-1-phosphate.
Lithium carbonate was shown to be an effective antimanic compound by John Cade in 1949, and this compound was approved for wide-spread use in 1969. However, treatment of manic-depressive patients with lithium is associated with certain deleterious side effects. These include tremor, weight gain, diarrhea, skin rash, transient leukocytosis, hypothyroidism, and polyuria-polydipsia. Additional clinical ailments associated with chronic lithium therapy are structural lesions in the kidney (including tubular atrophy, glomerular sclerosis and interstitial fibrosis). These side effects are directly due to lithium toxicity.
The phosphoinositide (PI) cycle is a likely target for lithium action, since it has been demonstrated that a profound elevation of inositol-1-phosphate and a corresponding decrease in free inositol in the brains of rats occurred when treated systemically with lithium. This was attributed to inhibition of inositol-1-phosphate phosphatase and led to the hypothesis that lithium was able to damp down the activity of the PI cycle in overstimulated cells, thus explaining its effectiveness in controlling mania.
Provision of inositol for the PI cycle can come from hydrolysis of inositol phosphates, by de novo synthesis from glucose, or from the diet. The former processes are dependent on the operation of inositol-1-phosphate phosphatase and are, therefore, inhibited by lithium. Dietary inositol can bypass lithium blockade in peripheral tissues but not in the CNS, since inositol does not cross the blood brain barrier. Thus, the increase in inositol-1-phosphate in brain is accompanied by an equivalent decrease in free inositol.
Manganese supports catalysis by inositol monophosphatase. on the other hand, divalent ions, i.e., calcium and manganese, are competitive inhibitors (Hallcher, L. M. and Sherman, W. R., J. Biol. Chem., 255:10896-901 (1980)). Lithium inhibits inositol monophosphate phosphatase uncompetitively.
IMP liberates inositol from the substrates INS (1) P, INS (3) P and INS (4) P. IMP is also capable of hydrolyzing various non-inositol containing substrates including but not limited to those disclosed by Sherman, J. Biol. Chem., 224:10896-10901 (1980), Takimoto, J. Bio. Chem. (Tokyo), 98:363-370 (1985) and by Gee, Bio. Chem J., 249:883-889 (1988). The first human IMP cDNA was isolated and is disclosed by McAllister et al., (WO 93/25692 (1993)).
The polypeptide of the present invention has been putatively identified as a human inositol monophosphatase polypeptide. This identification has been made as a result of amino acid sequence homology.
In accordance with one aspect of the present invention, there is provided a novel mature polypeptide, as well as biologically active and diagnostically or therapeutically useful fragments, analogs and derivatives thereof. The polypeptide of the present invention is of human origin.
In accordance with another aspect of the present invention, there are provided isolated nucleic acid molecules encoding a polypeptide of the present invention including mRNAs, DNAs, cDNAs, genomic DNAs as well as analogs and biologically active and diagnostically or therapeutically useful fragments thereof.
In accordance with yet a further aspect of the present invention, there is provided a process for producing such polypeptide by recombinant techniques comprising culturing recombinant prokaryotic and/or eukaryotic host cells, containing a nucleic acid sequence encoding a polypeptide of the present invention, under conditions promoting expression of said protein and subsequent recovery of said protein.
In accordance with yet a further aspect of the present invention, there is provided a process for utilizing such polypeptides, or polynucleotides encoding such polypeptides for therapeutic purposes, for example, for screening and designing compounds capable of inhibiting this class of enzymes, and for the treatment of psychiatric disorders.
In accordance with yet a further aspect of the present invention, there is provided an antibody against such polypeptides.
In accordance with yet another aspect of the present invention, there are provided antagonists against such polypeptides, which may be used to inhibit the action of such polypeptides, for example, in the treatment of psychotic and depressive disorders (bipolar and non-bipolar).
In accordance with yet a further aspect of the present invention, there is also provided nucleic acid probes comprising nucleic acid molecules of sufficient length to specifically hybridize to a nucleic acid sequence of the present invention.
In accordance with still another aspect of the present inventions there are provided diagnostic assays for detecting diseases or susceptibility to diseases related to mutations in the nucleic acid sequences encoding a polypeptide of the present invention.
In accordance with yet a further aspect of the present invention, there is provided a process for utilizing such polypeptides, or polynucleotides encoding such polypeptides, for in vitro purposes related to scientific research, for example, synthesis of DNA and manufacture of DNA vectors.
These and other aspects of the present invention should be apparent to those skilled in the art from the teachings herein.